1. Field of the Invention
The present invention relates to a broadcast receiving apparatus and broadcast receiving method for receiving digital broadcast and analog broadcast simultaneously, and particularly to a broadcast receiving apparatus and broadcast receiving method that can reduce uncomfortable auditory sensations caused by switching the output between the digital broadcast and the analog broadcast.
2. Description of the Related Art
Conventionally, technique of In Band On Channel (IBOC) has been known. IBOC is one type of audio broadcasting, according to which the frequency band used in FM broadcast and AM broadcast is employed to broadcast the same contents by both digital broadcasting and analog broadcasting simultaneously.
Digital broadcast signals used in digital broadcasting realize reproduction of contents in wider sound range than that realized by analog broadcast signals used in analog broadcasting. However, when using the digital broadcast signals, if the received field strength becomes lower than a predetermined level, the contents cannot be reproduced properly.
On the other hand, analog broadcast signals cannot realize reproduction of contents in as wide sound range as possible by the digital broadcast signals. However, the analog broadcast signals can reproduce broadcast programs even when the received field strength is as low as to inhibit the reproduction of contents by digital broadcast signals.
According to the IBOC, even when the contents cannot be reproduced by digital broadcast signals, it is still possible to reproduce the contents using the analog broadcast signals. A broadcast receiving apparatus, which receives the audio broadcast provided through the IBOC, switches the output from the digital broadcast to the analog broadcast if the reception status of the digital broadcast worsens during the output of the digital broadcast, and switches the output back to the digital broadcast when the reception status of the digital broadcast recovers.
However, the broadcast receiving apparatus which receives the audio broadcast provided through the IBOC sometimes causes an uncomfortable auditory sensation to the user when the output is switched from digital broadcast to analog broadcast or vice versa, because of the difference in sound range of the analog broadcast and the digital broadcast.
To lessen such uncomfortable auditory sensations, various broadcast receiving apparatuses are proposed. For example, Japanese Patent No. 4101719 (hereinafter referred to as “first document”) describes a broadcast receiving apparatus which, on determining that the reception status of the output of the digital broadcast is worsening and the output is going to be switched to the analog broadcast very soon, makes the acoustic characteristic of the digital broadcast gradually come close to the acoustic characteristic of the analog broadcast while the digital broadcast is being output.
More specifically, the broadcast receiving apparatus according to the first document determines that the output will be switched from the digital broadcast to the analog broadcast soon when the received field strength of the digital broadcast signal lowers to such a level that the reception status of the digital broadcast worsens.
Thus, the broadcast receiving apparatus of the first document reduces uncomfortable auditory sensations caused by switching the output from the digital broadcast to the analog broadcast by bringing the acoustic characteristic of digital broadcast close to the acoustic characteristic of analog broadcast before switching the output from digital broadcast to analog broadcast.
The broadcast receiving apparatus of the first document, however, cannot spare sufficient time for changing the acoustic characteristic. Hence, the uncomfortable auditory sensations caused by the output switching from one of digital broadcast and analog broadcast to the other cannot be reduced sufficiently.
More specifically, it is known that the reception status of digital broadcast suddenly worsens when the C/N ratio (Carrier to Noise ratio) of the received digital broadcast signal goes down below a predetermined C/N ratio, rather than linearly worsens along with the changes in received field strength of the digital broadcast signal.
Therefore, the broadcast receiving apparatus of the first document needs to bring the acoustic characteristic of digital broadcast close to the acoustic characteristic of analog broadcast rapidly within a very short time period after the reception status of digital broadcast starts worsening before the output is switched to analog broadcast.
The broadcast receiving apparatus of the first document is thus unable to reduce the uncomfortable auditory sensation caused by the output switching from digital broadcast to analog broadcast sufficiently.
Such problem also occurs when the output is switched from analog broadcast to digital broadcast. Therefore, the broadcast receiving apparatus of the first document may not be able to reduce the uncomfortable auditory sensations to a sufficient level when the output is switched from analog broadcast to digital broadcast.
In view of the foregoing, an issue now is how to realize the broadcast receiving apparatus and broadcast receiving method that would allow further reduction in uncomfortable auditory sensations that are caused by the output switching between digital broadcast and analog broadcast.
The present invention is made to solve the problems in the conventional technologies as described above, and an object of the present invention is to provide a broadcast receiving apparatus and a broadcast receiving method that allow further reduction in uncomfortable auditory sensations caused when the output is switched between digital broadcast and analog broadcast.